Check valve

ABSTRACT

A check valve ( 300 ) that opens and closes by causing a valve element ( 130 ) to come into contact with and separate from a valve seat ( 104 ) and thereby controls a flow of fluid that flows in through an inlet ( 101 ) and flows out through an outlet ( 102 ), having a guide portion ( 135 ) that has a fluid guide surface provided at a downside thereof, wherein the valve seat ( 104 ) has a first valve seat and a second valve seat, and the valve element ( 130 ) has a first valve portion ( 131 ) that is to be seated on the first valve seat, a second valve portion ( 132 ) that is to be seated on the second valve seat, and a pressure receiving surface ( 134 ) that extends between the first valve portion ( 131 ) and the second valve portion ( 132 ) in such a manner that a distance between the pressure receiving surface ( 134 ) and the first valve seat gradually reduces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.14/899,074, filed Dec. 16, 2015, which is a National Stage ofInternational Application No. PCT/JP2014/075981, filed Sep. 30, 2014(now WO2015/050091A1, published Apr. 9, 2015), which claims priority toJapanese Application No. 2013-207372, filed Oct. 2, 2013. The entiredisclosures of each of the above applications are incorporated herein byreference.

FIELD

The present disclosure relates to a check valve.

BACKGROUND

A low-temperature fluid pump for supplying a fluid having a lowerliquefaction temperature than air, such as liquid nitrogen, is mostlyused for feeding a fluid of a saturated vapor pressure (approximately 77K at atmospheric pressure), and is often configured to have a lowrequired net positive suction head (required NPSH) for the purpose ofpreventing vaporization of the fluid by negative pressure or the like.For this reason, it is preferred that a check valve used in a pump havea low flow rate resistance (high flow rate coefficient).

On the other hand, a positive displacement pump such as a bellows pumpdescribed in Patent Literature 1 is configured to increase the speed ofthe pump stroke or, in other words, to reduce the time required in onestroke, so that reduction in size and weight of the pump apparatus,especially the weight of the pump support member or bellows operatingshaft, can be realized, as well as reduction of the impact of the heatgenerated in the drive unit. Therefore, in order to achieve high-speedpump stroke, the time required by a behavior of a check valve used needsto be reduced. Specifically, in case of the poppet check valve describedin Patent Literature 2, it is required to reduce the time it takes forthe valve element to return by its own weight in a closure stroke.Moreover, a delay of the closure timing leads to a reverse flow of thefluid at valve closure, and the impact of a water hammer caused by thereverse flow is not negligible.

As a way to resolve a delay in valve closure, generally there is meansfor applying spring force in the return direction of the valve elementor reducing the degree of opening of the valve element at valve opening(check valve with a spring, etc.). There is also means, such as the onedescribed in Patent Literature 3, for forcibly closing the valve byusing external force of a cam, a solenoid, or the like. However,applying spring force or reducing the degree of opening leads to arelatively low flow rate coefficient of the valve, which means that thevalve needs to be enlarged to obtain a required flow rate coefficient,increasing the size of the pump itself. Furthermore, the configurationof forcibly closing the valve makes the mechanism complicated. Theconditions of a low-temperature use environment and thermal insulationneed to take into consideration, but such requirement makes it difficultto design the pumping mechanism.

The behavior of the valve element of a poppet check valve, on the otherhand, is known to have a great impact of the force acting on the valveelement due to the momentum of the fluid, as can be seen in the modelshown in FIGS. 12A and 12B. FIGS. 12A and 12B are schematic diagrams forexplaining the force acting on the valve element of the poppet valve.The force applied to the valve element is not only associated with thedifferential pressure ΔP (=P1-P2) between the upstream pressure (P1) andthe downstream pressure (P2) in the valve element but is also associatedwith the momentum of the fluid. The force acting on the valve element ofthe poppet valve is obtained by the following equation according to themodel shown in FIGS. 12A and 12B.

F=A·ΔP+ρ·Q·(V0−V·cos θ)  (1)

V=C/A·√(2/ρ·ΔP)  (2)

In these equations, A represents the cross-sectional area of the pipe(=π·d²/4), d represents the diameter of the pipe, ρ represents the fluiddensity, Q represents the flow rate (=V0·A), V0 represents the flowvelocity at the upstream, V represents the flow velocity at the valveportion, C represents the flow rate coefficient, and θ represents theangle formed by the tapered surface of the valve element and the axialline.

The first term on the right side of the equation (1) represents theforce caused by the differential pressure ΔP between the upstream andthe downstream, and the second term represents the force caused by themomentum of the fluid. In the structure of a self-weight operated valve,when the lift distance of the valve is substantially great with respectto the flow rate, V≈V0 is established. Therefore, as a result ofsubstituting the equation (2) and making adjustments, the equation (1)becomes as follows.

F=½·ρ·A·V0²·1/C ² +ρ·A·V0²·(1−cos θ)  (3)

The first term on the right side of the equation (3) represents theforce caused by the differential pressure ΔP between the upstream andthe downstream, and the second term represents the force caused by themomentum of the fluid. Compared to a valve that only has the action ofthe differential pressure ΔP and the same flow rate coefficient withrespect to the lift distance, the level of the force that pushes up thevalve element is higher by the level of the force represented by thesecond term, even when the flow rate is the same. This increases thetime it takes for the poppet valve to drop from its position at themaximum lift distance to the valve-closed position by its own weight,creating a delay of the closure timing.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Application Laid-open No.    2012-52617-   Patent Literature 2: Japanese Patent Application Laid-open No.    2008-95820-   Patent Literature 3: Japanese Patent Application Laid-open No.    S62-228679

SUMMARY Technical Problem

An object of the present disclosure is to provide a check valve capableof achieving a high-speed valve closing operation with a simpleconfiguration.

Solution to Problem

In order to achieve the foregoing object, the check valve of the presentdisclosure is a check valve that opens and closes by causing a valveelement to come into contact with and separate from a valve seat andthereby controls a flow of fluid that flows in through an inlet andflows out through an outlet, the check valve comprising: an inletprovided at a downside thereof; an outlet provided at an upside thereof;a valve seat formed to surround the inlet; a valve element configured tobe able to come into contact with and separate from the valve seatvertically; and a guide portion that has a fluid guide surface providedat a downside thereof, the fluid guide surface horizontally guiding afluid flown in from the inlet, and a valve element guide surfaceprovided on a side surface thereof, the valve element guide surfacevertically guiding the valve element.

According to the present disclosure, the level of force caused by themomentum of the fluid and acting on the valve element can be reduced.The flow direction of the fluid flowing in through the inlet is changedto a generally horizontal direction by the fluid guide surface of theguide portion. Because the force caused by the momentum of the fluidacts horizontally on the vertically moving valve element, the secondterm on the right side of the equation (3) is reduced. As a result, theforce that pushes up the valve element is lowered, as well as the liftdistance of the valve element, resulting in a reduction of the time ittakes for the valve element to drop from its position at the maximumlift distance to the valve-closed position by its own weight, as well asa delay of the closure timing.

It is preferred that the check valve further have an auxiliary valveelement that is configured to be able to be seated on the valve elementand the guide portion so as to cover a gap between the valve element andthe valve element guide surface when the valve element is seated on thevalve seat.

With the two-stage valve structure in which the gap between the valveelement and the guide portion is covered with the auxiliary valveelement after the valve element is seated, the impact of a water hammercaused by the reverse flow can be reduced. In other words, after thereverse flow rate is reduced with the valve of the first stage (thevalve element), the valve of the second stage (the auxiliary valveelement) is closed. This configuration can reduce the velocity of thereverse flow at valve closure, from which the magnitude of a waterhammer can be estimated.

It is preferred that the auxiliary valve element be mounted to the valveelement so as to be able to move vertically within a predeterminedrange, and a seating surface of the valve element on which the auxiliaryvalve element is seated and a seating surface of the guide portion onwhich the auxiliary valve element is seated are at a same height whenthe valve element is seated on the valve seat.

When the valve element is seated on the valve seat, the auxiliary valveelement gradually closes the gap between the valve element and the guideportion, reducing the impact of a water hammer more effectively.

It is preferred that the check valve further have a biasing member forbiasing the auxiliary valve element downward toward the valve elementand the guide portion.

According to this configuration, a high-speed valve closing operationcan be achieved due to the biasing force of the biasing member that actson the valve element via the auxiliary valve element in a valve closuredirection. In addition, by setting the biasing force accordingly, thecheck valve can be used as a check valve that makes the direction ofinstallation of the check valve opposite to the gravitational direction,i.e., a check valve that lets the fluid flow in one direction from theupper section to the lower section.

It is preferred that the valve element have a pressure receiving surfacethat extends outward from a lower end of an inner side surface guided bythe valve element guide surface, and extends horizontally with respectto the valve seat, or a pressure receiving surface that extends outwardfrom a lower end of an inner side surface guided by the valve elementguide surface, in such a manner that a distance between the pressurereceiving surface and the valve seat gradually reduces.

According to this configuration, the valve element is provided with apressure receiving surface extending along a direction generally alongthe flow direction of the fluid guided by the fluid guide surface.Therefore, almost no force is produced by the momentum of the fluidtowards the valve element, and the force acting on the valve element ismostly force resulting from the differential pressure (ΔP) between thepressure generated at the inlet side (the upstream pressure P1) and thepressure generated at the outlet side (the downstream pressure P2). Forthis reason, the second term on the right side of the equation (3) canbe reduced significantly.

It is preferred that a position of a gap between the valve element andthe guide portion be located outside the inlet as viewed vertically.

With this configuration in which the gap between the valve element andthe guide portion does not vertically overlap with the inlet, the fluidthat is flown in through the inlet changes its flow direction to ahorizontal direction first and then flows into the gap. Consequently,the impact of the momentum of the fluid acting on the auxiliary valveelement through the gap can be reduced, resulting in a more effectivereduction of the impact of a water hammer.

The valve seat may have a first valve seat and a second valve seat thatare configured such that flow directions therethrough of a fluid flowingfrom an upstream to a downstream when the valve is opened are oppositeto each other in a horizontal direction, and the valve element has afirst valve portion that is to be seated on the first valve seat, asecond valve portion that is to be seated on the second valve seat, anda pressure receiving surface that extends from the second valve portiontoward the first valve portion and extends between the first valveportion and the second valve portion in such a manner that a distancebetween the pressure receiving surface and the first valve seatgradually reduces.

According to this configuration, when the valve is opened, the directionin which the fluid flows in the first valve portion and the first valveseat and the direction in which the fluid flows in the second valveportion and the second valve seat becomes opposite to each other.Consequently the level of the force produced by the momentum of thefluid and acting on the valve element can be reduced.

Advantageous Effects of the Disclosure

According to the present disclosure, a high-speed valve closingoperation can be achieved with a simple configuration.

DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional diagrams of a check valveaccording to Example 1 of the present disclosure;

FIG. 2 is a partial enlarged view of FIG. 1;

FIG. 3 is a schematic configuration diagram of a liquid supply system;

FIGS. 4A and 4B are schematic cross-sectional diagrams of a modificationof the check valve according to Example 1 of the present disclosure;

FIGS. 5A and 5B are schematic cross-sectional diagrams of a check valveaccording to Example 2 of the present disclosure;

FIG. 6 shows a measurement result of a closing response time of thecheck valve according to Example 2 of the present disclosure;

FIG. 7 shows a measurement result of a closing response time accordingto a conventional check valve;

FIG. 8 shows a measurement result of water hammer force in the checkvalve according to Example 2 of the present disclosure;

FIG. 9 shows a measurement result of the level of water hammer force inthe conventional check valve;

FIGS. 10A and 10B are schematic cross-sectional diagrams showing a checkvalve according to Example 3 of the present disclosure;

FIGS. 11A and 11B are partial enlarged views of FIG. 10A; and

FIGS. 12A and 12B are schematic diagrams for explaining force acting ona valve element of a poppet valve.

DETAILED DESCRIPTION

Hereinafter, modes for carrying out the present disclosure will beexemplarily described in detail based on examples thereof with referenceto the drawings. However, the dimensions, materials, shapes, relativearrangements and so on of constituent parts described in the examplesare not intended to limit the scope of the present disclosure to thesealone in particular unless specifically described.

Example 1

A liquid supply system having a check valve according to an example ofthe present disclosure is described with reference to FIG. 3. FIG. 3 isa schematic configuration diagram of the liquid supply system having thecheck valve according to the example of the present disclosure.

<Liquid Supply System>

A liquid supply system 10 is a low-temperature fluid pump apparatus, inwhich extremely cold liquid L is constantly supplied to a resincontainer 31 of a cooled device 30 having a superconducting coil 32, inorder to keep the superconducting coil 32 in a superconducting state.Specific examples of the extremely cold liquid L include liquid nitrogenand liquid helium.

The liquid supply system 10 has a first container 11 for storing theextremely cold liquid L, a second container 12 that is disposed in theliquid L stored in the first container 11, and a bellows 13 placedinside the second container 12. A region outside the bellows 13 in thesecond container 12 configures a first pump chamber P1. The inside ofthe bellows 13 is an enclosed space which configures a second pumpchamber P2. The second container 12 is provided with a first suctionport 21 through which the liquid L of the first container 11 isintroduced into the first pump chamber P1, and a first feed port 22through which the introduced liquid L is fed from the first pump chamberP1 to a supply passage (supply pipe) K1 leading to the outside of thesystem. The second container 12 is also provided with a second suctionport 23 through which the liquid L of the first container 11 isintroduced into the second pump chamber P2, and a second feed port 24through which the introduced liquid L is fed from the second pumpchamber P2 to the supply passage K1. The first suction port 21 and thesecond suction port 23 are provided respectively with check valves 100 aand 100 c according to the present example, and the first feed port 22and the second feed port 24 are provided respectively with check valves100 b and 100 d according to the present example.

A shaft 15, configured to reciprocate by a linear actuator 4 functioningas a drive source, enters the bellows 13 from the outside of the firstcontainer 11, to have a tip thereof secured to a tip of the bellows 13.Thus, the reciprocal movement of the shaft 15 expands and contracts thebellows 13.

An enclosed space R1 filled with a gas is formed around the shaft 15.This enclosed space R1 is configured with a tubular (preferablycylindrical) pipe portion 61 that extends from the outside of the firstcontainer 11 to reach the bellows 13 and has the shaft 15 insertedtherethrough, and small bellows 62 and 63 that are provided at a lowerend portion and an upper end portion of this pipe portion 61respectively. The small bellows 63 separating the enclosed space R1 fromthe second pump chamber P2 and the small bellows 63 separating theenclosed space R1 from the external space are secured to the shaft 15 attheir tips and configured to expand and contract as the shaft 15reciprocates. The small bellows 62, 63 are each configured to have anouter diameter smaller than that of the bellows 13.

The upper-end side of the bellows 13, too, is provided with the smallbellows 62 as described above, so the inside of the bellows 13 is anenclosed space, which, as described above, configures the second pumpchamber P2.

According to the foregoing configuration, when the bellows 13 contracts,the liquid L is fed from the second pump chamber P2 to the supplypassage K1 through the second feed port 24 and introduced into the firstpump chamber P1 through the first suction port 21. When the bellows 13expands, the liquid L is introduced into the second pump chamber P2through the second suction port 23 and fed from the first pump chamberP1 to the supply passage K1 through the first feed port 22. In eithercase where the bellows 13 contracts or expands, the liquid L is fed tothe supply passage K1.

In the liquid supply system 10, as described above, the bellows 13expands and contracts repeatedly, thereby supplying the liquid L to thecooled device 30 through the supply passage K1. There is also provided areturn passage (return pipe) K2 that links the liquid supply system 10and the cooled device 30. The return passage K2 is configured such thatthe liquid L returns to the liquid supply system 10 as much as issupplied to the cooled device 30. A cooler 20 is provided in the middleof the supply passage K1 in order to cool the liquid L to an extremelylow temperature. According to such configuration, the liquid L that iscooled to an extremely low temperature by the cooler 20 circulatesbetween the liquid supply system 10 and the cooled device 30.

As described above, in either case where the bellows 13 contracts orexpands, the liquid L is fed to the supply passage K1, and the amount ofliquid supplied by the expansion and contraction of the bellows 13 canbe made twice the amount obtained by the pumping function of the firstpump chamber P1 alone. Therefore, compared to when the pumping functionof the first pump chamber P1 alone is fulfilled for a desired amount ofliquid supplied, the amount of liquid supplied at once can be reduced tohalf, and consequently the maximum pressure of the liquid in the supplypassage K1 can also be reduced to approximately half. As a result, thenegative impact of a pressure fluctuation (pulsation) of the suppliedfluid can be curbed.

In addition, the liquid L is supplied continuously, preventing thepulsation itself. Therefore, unlike a configuration in which a buffer(damper) is provided outside the system, space saving can be realizedand areas where heat exchange takes place can be reduced, improving thecooling efficiency.

The enclosed space R1 of the tubular pipe portion 61 through which theshaft 15 is inserted is structured to be filled with a gas. Suchstructure allows the enclosed space R1 filled with a gas to function tohinder heat transfer, preventing heat or atmospheric heat generated bythe linear actuator 14 from being transmitted to the liquid L. Even ifthe heat is transmitted to the liquid L, new liquid L is constantlysupplied, bringing about the cooling effect and preventing thetemperature inside the pump chambers from increasing to the temperatureat which the liquid L evaporates. Therefore, the pumping function doesnot deteriorate.

Moreover, if by any chance heat or the like from the shaft 15 causes theliquid L of the bellows 13 to evaporate into a gas and consequently thepumping function of the second pump chamber P2 deteriorates, the pumpingfunction of the first pump chamber P1 can stably be exerted.Furthermore, unlike when the inside of the bellows is filled with a gas(being compressible fluid), the configuration according to the presentexample has the liquid L (being non-compressible fluid) present both onthe inside and outside of the bellows 13 and can therefore prevent thebellows 13 from whirling or buckling when the bellows 13 expands.

The enclosed space R1 is also configured with the pipe portion 61 andthe pair of small bellows 62, 63. The small bellows 62, 63 are securedto the shaft 15 at their tips so as to be able to expand and contract asthe shaft 15 reciprocates. Providing the enclosed space R1 withoutcreating a sliding section can prevent generation of heat accompanied bya frictional resistance triggered by sliding.

The present example has described a configuration in which the enclosedspace R1 is filled with a gas; however, a configuration can be employedin which the inside of the enclosed space R1 is evacuated. Evacuatingthe inside of the enclosed space R1 can further enhance the heatinsulation effect.

<Check Valve>

A check valve according to Example 1 of the present disclosure is nowdescribed with reference to FIGS. 1A, 1B and 2. FIGS. 1A and 1B areschematic cross-sectional diagrams of the check valve according toExample 1 of the present disclosure, in which FIG. 1A shows a closedstate of the valve and FIG. 1B shows an open state of the valve. FIG. 2is a partial enlarged view of FIG. 1A, showing a configuration of theperiphery of an auxiliary valve element.

A check valve 100 according to the present example is a one-way valve inwhich fluid (liquid L) flows in through an inlet 101 provided at thedownside of the check valve and flows out of an outlet 102 provided atthe upside of the check valve, allowing the fluid to flow only in adirection opposite to the gravitational direction (vertical direction).In case of a double reciprocating bellows pump for low-temperaturefluid, such as the one shown in FIG. 3, the check valve 100 according tothe present example is provided on two locations on the discharge sideand two locations on the suction side.

<Configuration of the Check Valve>

A valve main body 103 formed generally into a cylinder, the inlet 101,and a valve seat 104 are formed in the check valve 100. The inlet 101 isopened upward in an internal region of the valve main body 103, and thevalve seat 104 is formed into a horizontal annular shape in the outercircumference of the inlet 101. A column member 105 that functions asthe guide portion is inserted into and positioned in a spigot jointportion provided between the inlet 101 and the valve seat 104, and ispressed down from above and secured by a metal holder 106.

The metal holder 106 has a plurality of holes 107 penetrating verticallyand is mounted with its outer circumferential end being held securelybetween a substantially tubular lid 108 with the outlet 102 and thevalve main body 103. The lid 108 and the valve main body 103 are joinedto each other by a tightening member 109 such as a nut, and the jointsurface therebetween is sealed with a gasket 110. A gasket for sealingthe joint surface is generally a Teflon-type gasket but may be a metalgasket. The gasket may not be used, depending on the allowance of fluidleakage to the outside. The shape of the holes 107 is not particularlylimited and therefore may have a circular (perfect circle, ellipse,etc.) or rectangular cross section; thus, various configurations can beemployed.

A valve element 112, an annular member, is mounted on a guide surface(valve element guide surface) 111, which is an outer circumferentialsurface of the column member 105, so as to be able to move vertically(axially). The valve element 112 forms an annular sealing surface bybringing a projection 113, an annular abutting portion provided at thebottom of the valve element 112, to come into abutment with the annularvalve seat 104, establishing the closed state. With the presence of thisconvex projection 113, the face pressure of the contact surface can beincreased in the airtight state in which the valve element is seated onthe valve seat 104. In addition, an auxiliary valve element 114 forsealing the gap between the valve element 112 and the column member 105is mounted in the upper part of the valve element 112.

The column member 105 has, at its lower part, a cutout groove 115 formedin an axially symmetric manner and extending radially from the center ofthe column member 105, and forms, along with a lower surface 116, aguide flow path for horizontally guiding the fluid that flows from thedownside to the upside through the inlet 101.

For the purpose of enabling a smooth vertical movement, the valveelement 112 is fitted (loose-fit), with a predetermined gap between theguide surface 111 of the column member 105 and an inner circumferentialsurface 117 functioning as a guided surface. In addition, an annular,horizontal pressure receiving surface (fluid guide surface) 118 isformed on the inside of the projection 113.

The auxiliary valve element 114, a disk-shaped plate member with a holeat the center, is held by a retaining member 119, with a gap Gtherebetween that enables a vertical movement of the auxiliary valveelement 114 within a predetermined range with respect to an uppersurface 120 of the valve element 112 (FIG. 2). The auxiliary valveelement 114 is also configured in such a manner that an innercircumferential surface 121 can come into vertically slidable contactwith an outer circumferential surface 122 of the metal holder 106. Theupper surface 120 of the valve element 112 and an upper surface 123 ofthe column member 105 are at the same height when the valve element 112is seated. According to this configuration, the auxiliary valve element114 can be seated on the upper surface 120 of the valve element 112 andthe upper surface 123 of the column member 105 in such a manner as tocover the gap between the inner circumferential surface 117 of the valveelement 112 and the guide surface 111 of the column member 105 withrespect to the outlet 102. Basically the auxiliary valve element 114 maynot only be a plate but may also be a hole, a groove, a cutout, and thelike. Also, the sealing position can be adjusted by forming an unevenportion extending toward the center. In terms of not to inhibit theauxiliary valve element 114 from bending along (becoming deformed along)the uneven surface (the difference in height) between the upper surfaceof the valve element 112 functioning as the valve seat and the uppersurface 123 of the column member 105 when the valve is closed, the sizeof the gap G formed between the retaining member 119 and the uppersurface 120 of the valve element 112 is set to be the minimum possiblesize in anticipation of deformation of an outer circumferential portionof the auxiliary valve element 114 so that the outer circumferentialportion is not confined (so that the outer circumferential portion canbe deformed sufficiently). Even when the outer circumferential portionof the auxiliary valve element 114 is confined (fixed), the gap G doesnot have to be provided as long as deformation along the uneven portionof the valve seat is guaranteed.

Because the liquid supply system is used in an environment withextremely low temperature, the components configuring the check valve100 according to the present example are preferably made of, in case ofmetals, austenitic stainless steel, titanium, or aluminum because thesematerials do not fracture at relatively low temperature. In case ofresins, it is preferred that the components be made of PTFE,polyimide-based resin or other materials, the mechanical characteristicsof which do not deteriorate significantly at low temperature. Inaddition, due to the temperature difference of 200° C. or higher betweenthe normal temperature and the operating temperature as well as due tothermal contraction of the members under the operating temperature, itis preferred that the operating portions with gaps such as the valveelement 112, the auxiliary valve element 114 and the column member 105be made of the same material or of a combination of materials thatincrease the gaps. Moreover, the contact surface of the valve element orvalve seat and the moving portions such as the valve element, auxiliaryvalve element or column member may be subjected to a heat treatment or asurface treatment (Teflon coating, silver plating, vapor deposition) inorder to reduce wear.

<Closing/Opening Operation of Check Valve>

In the check valve 100, when the force caused by the fluid pressure P1at the inlet 101 side becomes smaller than the force caused by theweight of the valve element 112 and the fluid pressure P2 at the outlet102 side, the valve element 112 drops by its own weight, establishingthe closed state. When the force caused by the fluid pressure P1 at theinlet 101 side becomes greater than the force caused by the weight ofthe valve element 112 and the fluid pressure P2 at the outlet 102 side,the valve element 112 is lifted off the valve seat 104, establishing theopen state.

The fluid that flows from the downside to the upside through the inlet101 is guided horizontally by the guide flow path configured by thegroove 115 and lower surface 116 of the column member 105. An annularflow path is formed on the downstream side of a downstream opening (anopening on the outer circumferential side of the groove 115) of theguide flow path by the valve seat 104, the projection 113 of the valveelement 112, the pressure receiving surface 118, and the outercircumferential surface (guide surface 111) of the column member 105.When the force that is applied to the valve element 112 due to thepressure P1 in this flow path becomes greater than the force that isapplied to the valve element 112 due to the weight of the valve element112 and P2, the valve element 112 rises and separates from the valveseat 104 as the pressure P1 is received by the pressure receivingsurface 118. At this moment, the auxiliary valve element 114 is alsolifted off the valve element 112 by the pressure P1 of the fluid flowingthrough the gap between the column member 105 and the valve element 112,forming a small flow path communicating the inlet 101 to the outlet 102.The auxiliary valve element 114 further separates from the upper surface123 of the column member 105 while sliding along the outercircumferential surface 122 of the metal holder 106, as the valveelement 112 rises.

<Advantages of Present Example>

According to the valve structure of the check valve 100 according to thepresent example, the force acting on the valve element 112 is mostly theforce that is caused by the differential pressure ΔP between theupstream pressure (P1) and the downstream pressure (P2) and acting onthe pressure receiving surface 118, i.e., the annular region surroundedby the lower rim of the inner circumferential surface 117 of the valveelement 112 and the projection 113. Although the projection 113 issubjected to a pressure acting radially outward, the level of thepressure is lower than that of the pressure received by the pressurereceiving surface 118, thus having less impact on the behavior of thevalve element 112. The momentum of the fluid acting on the valve element112 is basically applied in the radial direction of the valve element112 by the guide flow path described above so that the axial force actsslightly on the projection 113; hence it is lowered more significantlyas compared to the poppet valve shown in FIGS. 12A and 12B. The valveelement 112, therefore, is lifted mainly by the pressure received by thepressure receiving surface 118.

The momentum of the fluid acts in the radial direction in an axiallysymmetric manner and is therefore offset in terms of the force to beadded to the valve element 112. In other words, the second term on theright side of the equation (3) that expresses the force F acting on thepoppet valve is reduced significantly. As a result, the force thatpushes up the valve element 112 becomes lower than that of the poppetvalve; thus reducing the lift distance of the valve element 112.Consequently, the time it takes for the valve element 112 to drop fromits position at the maximum lift distance to the valve-closed positionby its own weight is shortened, reducing a delay of the closure timing.

As described above, high-speed pumping can be realized by reducing adelay of the closure timing of the check valve. This point is describedbelow.

In case of a positive displacement pump such as the bellows pump shownin FIG. 3, the flow rate thereof has the following relation. Q=Vth×N×n

In the foregoing equation, Q represents the flow rate [l/min], Vthrepresents the stroke volume [l], N represents the number of strokes[cpm], and n represents the volumetric efficiency.

According to this relation, when the flow rate is constant, the higherthe number of strokes N is, the lower the required stroke volume Vthbecomes. The lower the stroke volume Vth is, the lower the stroke volumeof the bellows becomes. When the bellows stroke volume is low, thebellows effective area, which is obtained based on a possible bellowsstroke as designed, can be reduced. Accordingly, rigidity that isrequired for the members involved in the operation of the bellows can bereduced by lowering the bellows test load obtained by a formula,“Bellows Effective Area (Ab)×(Pump Discharge Pressure P)”. As a result,the pump support member and a bellows operating shaft member can be madelighter.

Making the pump support member and the bellows operating shaft lightercan reduce the coefficient of heat transfer generated in the apparatusaxial direction of the pump, resulting in a structural reduction of theamount of heat that enters the low-temperature liquid stored in the tankfrom the atmosphere. Such configuration is preferred because it canlower the evaporation rate of the low-temperature liquid and thenecessary cooling capacity of, for example, a refrigerator.

The light-weighted, compact pump is preferred as it can improve theeasiness to handle, the saving of installation space, the resistance tovibration, and the resistance to shock.

For these reasons, high-speed pumping (reducing the time required in onestroke) is favorable to a low-temperature pump. In high-speed pumping, alag time of the closure timing of the check valve is largely related tothe discharging performance (volumetric efficiency) of the pump. Whenthere is a delay of the closure timing of the check valve (when the lagtime is long), the fluid that is discharged (suctioned) during the lagtime period of the closure of the check valve flows backwards, resultingin a reduction of the volumetric efficiency. In some cases, the impactof a water hammer caused by the closure of the valve during the reverseflow is not negligible. In case of accelerated pumping in which the timerequired in one stroke is reduced, when the lag time of the closure ofthe valve is equal to the time required in one stroke, the amount ofliquid discharged and the reverse flow rate become substantially thesame, which is the limit of the high-speed pumping. Thus, reducing thelag time of the closure of the check valve largely contributes to theimprovement of the cycle of limiting the high-speed pumping.

According to the present example, therefore, high-speed pumping can beachieved by reducing a lag time of the closing of the check valve.

The present example employs the two-stage valve structure in which a gapis provided between the valve element 112 and the column member 105 toenable the valve element 112 to move smoothly and the gap is closed withthe auxiliary valve element 114 after the valve element 112 is seated.According to this two-stage valve structure, the impact of a waterhammer caused by the reverse flow of the liquid can be reduced more ascompared with a one-stage valve structure. This is because after thereverse flow rate is reduced by the valve (the valve element 112) of thefirst stage, the valve of the second stage (the auxiliary valve element114) is eventually closed, thereby reducing the velocity of the reverseflow at valve closure which is an indication of the magnitude of a waterhammer.

Further, due to the configuration in which the position of the gapbetween the valve element 112 and the column member 105 is locatedoutside the inlet 101 as viewed vertically (the gap does not verticallyoverlap with the inlet 101), the fluid that flows in through the inlet101 firstly changes its flow direction to the horizontal direction andthen flows into the gap. Consequently, the impact of the momentum of thefluid acting through the gap on the auxiliary valve element 114 can bereduced, resulting in a more effective reduction of the impact of awater hammer.

According to the valve structure of the present example, the pressure ofopening the valve is determined based on the relationship between theflow rate and the weight of the valve element 112 without changing thesize of the flow path on the inlet 101 side, by appropriately adjustingthe sealing position of the valve element 112 (the position where theprojection 113 comes into abutment with the valve seat 104) in theradial direction of the valve element 112. Therefore, the pressure ofopening the valve can be adjusted properly.

The lift distance of the valve is also roughly determined based on therelationship between the flow rate and the weight of the valve element112 without changing the diameter of the flow path on the inlet 101side, by appropriately adjusting the sealing position of the valveelement 112 in the radial direction of the valve element 112. Therefore,the lift distance of the valve can be adjusted properly.

In addition, the pressing force that is produced by ΔP generated at thetime of closing the valve can be adjusted without changing the diameterof the flow path on the inlet 101 side, by appropriately adjusting thesealing position of the valve element 112 in the radial direction of thevalve element 112. Because excessive level of pressing force expediteswear of the valve as a result of repeated contact between the valveelement 112 and the valve seat 104, adjusting the pressing force can notonly reduce wear but also improve durability of the valve.

<Modification>

FIGS. 4A and 4B are schematic cross-sectional diagrams of a modificationof the check valve of the present example, in which FIG. 4A shows aclosed state of the valve and FIG. 4B shows an open state of the valve.As in the modification, a spring 124 functioning as the biasing memberfor biasing the auxiliary valve element 114 downward may be mountedvertically in a compressed state between the upper surface of theauxiliary valve element 114 and the lower end surface of the metalholder 106. According to this modification, the biasing force of thespring 124 acts on the valve element 112 through the auxiliary valveelement 114 in a valve closing direction, facilitating a high-speedvalve closing operation. In addition, by setting the spring loadaccordingly, the direction of installation of the check valve 100 can bemade opposite to the gravitational direction. In other words, the fluidcan be let flow in one direction from the upside to the downside.

Example 2

A check valve according to Example 2 of the present disclosure isdescribed with reference to FIGS. 5A and 5B. FIGS. 5A and 5B areschematic cross-sectional diagrams of the check valve according toExample 2, in which FIG. 5A shows a closed state of the valve and FIG.5B shows an open state of the valve. The following mainly discusses thedifferences from Example 1, in which the same reference numerals areused to describe the components same as those of Example 1, and thedescriptions thereof are omitted accordingly. The matters that are notdescribed below are the same as those of Example 1.

A check valve 200 according to the present example has a differentconfiguration of a valve element from that of the check valve 100 ofExample 1. A valve element 125 of the present example has a taperedpressure receiving surface 126. The pressure receiving surface 126 is aninclined surface extending from the lower end of the innercircumferential surface of the valve element 125 in such a manner thatthe distance between the pressure receiving surface 126 and the valveseat 104 in the vertical direction gradually reduces toward the outerdiameter, in which the outer circumferential end of the pressurereceiving surface 126 configures an annular abutting portion 127 that isin abutment with the valve seat 104. In this configuration, as inExample 1, the level of the force caused by the momentum of the fluidand acting on the valve element 125 can be reduced.

The angle of the pressure receiving surface 126 is set to an angle inwhich a horizontal force component of the force acting on the pressurereceiving surface 126 becomes greater than a vertical force component,i.e., an angle in which the level of the force caused by the momentum ofthe fluid and acting on the valve element 125 can be lowered as much aspossible. For instance, the angle of the pressure receiving surface 126can be set to an angle as shallow as 10° with respect to a horizontalplane. From the same perspective, the height of the projection 113according to Example 1 may be set to have approximately the same heightdifference with the pressure receiving surface 118 as the heightdifference between the inner circumferential end and the outercircumferential end of the tapered surface.

The pressure receiving surface 126 may be configured as a reversetapered surface, i.e., an inclined surface that extends from the lowerend of the inner circumferential surface of the valve element 125 insuch a manner that the distance between the pressure receiving surface126 and the valve seat 104 in the vertical direction gradually increasestoward the outer diameter. It should be noted that the angle of thepressure receiving surface 126 is set so as not to increase the level ofthe force that acts radially outward on the inner circumferentialsurface of the abutting portion 127, i.e., the force caused by themomentum of the fluid and acting on the valve element 125.

Further, in the present example, a spacer 128 is used to regulate therange of vertical movement of the auxiliary valve element 114, withoutusing the retaining member 119 of Example 1. The spacer 128 is securedto the upper surface of the auxiliary valve element 114 and has apredetermined thickness. This configuration can reduce the impact of awater hammer caused when the fluid flows backward, as with Example 1.

<Comparative Experiments>

With reference to FIGS. 6 to 9, the following describes the effects ofshortening the closing response time and the effects of reducing theimpact of a water hammer according to the present example. FIG. 6 is adiagram showing a measurement result of the closing response time of thecheck valve according to Example 2. FIG. 7 is a diagram showing ameasurement result of the closing response time of a conventional checkvalve. FIG. 8 is a diagram showing a measurement result of the level ofthe impact of a water hammer in the check valve according to Example 2.FIG. 9 is a diagram showing a measurement result of the level of theimpact of a water hammer in the conventional check valve.

A check valve in which the angle of the tapered surface is approximately10°, the pressure receiving area is approximately 10 cm², the maximumoperating range of the valve element is approximately 3 mm, and theeffective diameter of the valve element is 25 mm, was used as the checkvalve of the present example. Also, a poppet valve having the sameeffective diameter as the check valve of the present example was used asthe conventional check valve.

<<Comparison of Closing Response Times>>

The strokes of the bellows and valve element (valve) in the check valveof the present example and the puppet valve as the conventional valvewere measured with a displacement meter, and the time it took for thevalve element to drop from the lowest point (bottom dead center) of thebellows stroke to its seating point was measured as the closing responsetime. While the closing response time of the conventional poppet valvewas 21 ms as shown in FIG. 7, the closing response time of the checkvalve of the present example was 12 ms as shown in FIG. 6, aconsiderable reduction of the closing response time.

<<Comparison of Levels of Water Hammers>>

Pressure gauges were installed at the upstream side and the downstreamside of each valve element (valve), to measure a water hammer pressuregenerated at valve closure. As shown in FIG. 9, in the conventionalpoppet valve, a pressure of −120 KPa was generated at the inlet sidewith respect to a line pressure (100 KPa), whereas at the outlet side, apressure of +460 KPa was generated with respect to the line pressure. Inthe check valve of the present example, on the other hand, the pressuregenerated at the inlet side was −100 KPa with respect to the linepressure, whereas the pressure generated at the outlet side was +210 KPawith respect to the line pressure, as shown in FIG. 8, meaning that theimpact of the water hammer was reduced significantly.

Example 3

A check valve according to Example 3 of the present disclosure is nowdescribed with reference to FIGS. 10A to 11B. FIGS. 10A and 10B areschematic cross-sectional diagrams of the check valve according toExample 3 of the present disclosure, in which FIG. 10A shows a closedstate of the valve and FIG. 10B shows an open state of the valve. FIGS.11A and 11B are partial enlarged views of FIG. 10A, showing theconfiguration of the periphery of the valve element, in which FIG. 11Ashows a state where only a first valve portion is closed and FIG. 11Bshows a state in which the first valve portion and a second valveportion are closed. The following mainly discusses the differences fromExample 1 and Example 2, in which the same reference numerals are usedto describe the components same as those of Examples 1 and 2. Thematters that are not described below are the same as those of Examples 1and 2.

A check valve 300 according to the present example has differentconfigurations of a valve element and a column member from those of thecheck valves 100 and 200 according to Examples 1 and 2 and does not havean auxiliary valve element. As shown in FIGS. 10A and 10B, a valveelement 130 of the present example has a first valve portion 131 with alarge diameter, a second valve portion 132 with a small diameter, and aninclined portion 134 that stretches out in the form of an umbrella fromthe second valve portion 132 and continues to the first valve portion131. An annular weight 133 is connected to the upper surface of thesecond valve portion 132. The valve element 130 is made of anelastically deformable material, such as SUS or resin, which is notaffected by the fluid inside.

The first valve portion 131 of the valve element 130 is seated on thevalve seat 104 to form a first annular sealing surface. The lowersurface of the inclined portion 134 of the valve element 130 configuresa tapered pressure receiving surface. A column member 135 of the presentexample has a flange portion 137 at its lower end, in which the uppersurface of the flange portion 137 configures a valve seat for the secondvalve portion 132 of the valve element 130. The lower surface of theflange portion 137 functions as the fluid guide surface for guiding thefluid that flows in through the inlet 101 radially outward. The secondvalve portion 132 is seated on the upper surface of the flange portion137, configuring a second annular sealing surface. Note that a metalholder 136 of the present example has a different shape from the metalholder 106 of Examples 1 and 2 but satisfies the same required function.

In the check valve 300, when the force caused by the fluid pressure P1at the inlet 101 side becomes smaller than the force caused by theweight of the valve element 130 and the fluid pressure P2 at the outlet102 side, the valve element 130 drops by its own weight, establishingthe closed state. The weight 133 is provided to allow the valve element130 to drop by its own weight, and the weight of the valve elementitself may be adjusted by providing a thick portion in the second valveportion 132 instead of providing the weight 133.

At valve closure, the first valve portion 131 is seated on the valveseat 104 first but the second valve element 132 is not seated, as shownin FIG. 11A. Subsequently, the entire valve element 130 creates elasticdeformation based on the seated first valve portion 131, whereby thesecond valve portion 132 is seated on the upper surface of the flangeportion 137.

Specifically, as shown in FIG. 11B, the periphery of the first valveportion 131 that is first seated creates diametrically expandingdeformation, which shifts the seating position of the first valveportion 131 to the outside (the sealing surface expands diametrically),and the inclined portion 134 deforms by bending inward. At the sametime, the second valve portion 132 and the weight 133 drop whileslightly creating diametrically contracting deformation and are seatedon the upper surface of the flange portion 137. As there is a gapbetween the inner circumferential surface of the second valve portion132 and the outer circumferential surface of the column member 135, anannular flow path is formed. At valve closure, the second valve portion132 is seated on the upper surface of the flange portion 137 whilenarrowing down the annular flow path.

At valve opening, when the force caused by the fluid pressure P1 at theinlet 101 side becomes greater than the force caused by the weight ofthe valve element 130 and the fluid pressure P2 at the outlet 102 side,the first valve portion 131 and second valve portion 132 of the valveelement 130 are lifted off the valve seat 104 and the upper surface ofthe flange portion 137, establishing the open state.

The check valve 300 according to the present example has the two-stagevalve structure in which the second valve portion 132 is closed afterthe first valve portion 131 is closed. Furthermore, the direction inwhich the fluid flows in the first valve portion 131 and the directionin which the fluid flows in the second valve portion 132 are opposite toeach other. In other words, the fluid that flows in through the inlet101 changes its flow direction to a horizontally outward directionfirst, then changes its flow direction to a horizontally inwarddirection, and then flows into the second valve portion 132. The lowersurface of the inclined portion 134 configuring the pressure receivingsurface extends from the inner circumference of the valve element 130 insuch a manner that the distance between the inclined portion 134 and thevalve seat 104 in the vertical direction gradually reduces toward theouter diameter. Owing to this configuration, the present example canreduce the level of the force produced by the momentum of the fluid andacting on the valve element 130, as in Examples 1 and 2.

With respect to the above described examples, it is possible to employthe constituent components of each of the examples in combination.

REFERENCE SIGNS LIST

-   Check valve 300-   Inlet 101-   Outlet 102-   Valve main body 130-   First valve portion 131-   Second valve portion 132-   Inclined portion 134-   Valve seat 104-   Column member (guide portion)135-   Metal holder 136-   Hole 107-   Lid 108-   Groove 115

What is claimed is:
 1. A check valve that opens and closes by causing avalve element to come into contact with and separate from a valve seatand thereby controls a flow of fluid that flows in through an inlet andflows out through an outlet, the check valve comprising: an inletprovided at a downside thereof; an outlet provided at an upside thereof;a valve seat formed to surround the inlet; a valve element configured tobe able to come into contact with and separate from the valve seatvertically; and a guide portion that has a fluid guide surface providedat a downside thereof, the fluid guide surface horizontally guiding afluid flowing in through the inlet, and a valve element guide surfaceprovided on a side surface thereof, the valve element guide surfacevertically guiding the valve element, wherein the valve seat has a firstvalve seat and a second valve seat that are configured such that flowdirections therethrough of a fluid flowing from an upstream to adownstream when the valve is opened are opposite to each other in ahorizontal direction, and the valve element has a first valve portionthat is to be seated on the first valve seat, a second valve portionthat is to be seated on the second valve seat, and a pressure receivingsurface that extends from the second valve portion toward the firstvalve portion and extends between the first valve portion and the secondvalve portion in such a manner that a distance between the pressurereceiving surface and the first valve seat gradually reduces.